Towards the predictive modeling of ductile failure

Gross, Andrew Jeffrey

Towards the predictive modeling of ductile failure

dc.contributor.advisor	Ravi-Chandar, K.	en
dc.contributor.committeeMember	Kovar, Desiderio	en
dc.contributor.committeeMember	Landis, Chad	en
dc.contributor.committeeMember	Liechti, Kenneth	en
dc.contributor.committeeMember	Kyriakides, Stelios	en
dc.creator	Gross, Andrew Jeffrey	en
dc.creator.orcid	0000-0001-7024-1342	en
dc.date.accessioned	2016-02-09T18:17:27Z	en
dc.date.available	2016-02-09T18:17:27Z	en
dc.date.issued	2015-12	en
dc.date.submitted	December 2015	en
dc.date.updated	2016-02-09T18:17:27Z	en
dc.description.abstract	The ability to predict ductile failure is considered by an experimental examination of the failure process, validation exercises to assess predictive ability, and development of a coupled experimental-numerical strategy to enhance model development. In situ loading of a polycrystalline metal inside a scanning electron microscope is performed on Al 6061-T6 that reveals matrix-dominated response for both deformation and failure. Highly localized deformation fields are found to exist within each grain as slip accumulates preferentially on a small fraction of crystallographic planes. No evidence of damage or material softening is found, implying that a strain-to-failure model is adequate for modeling fracture in this and similar material. This modeling insight is validated through blind predictive simulations performed in response to the 2012 and 2014 Sandia Fracture Challenges. Constitutive and failure models are calibrated and then embedded in highly refined finite element simulations to perform blind predictions of the failure behavior of the challenge geometries. Comparison of prediction to experiment shows that a well-calibrated model that captures the essential elastic-plastic constitutive behavior is necessary to capture confidently the response for structures with complex stress states, and is a prerequisite for a precise prediction of material failure. The validation exercises exposed the need to calibrate sophisticated plasticity models without a large experimental effort. To answer this need, a coupled experimental and numerical method is developed for characterizing the elastic-plastic constitutive properties of ductile materials using local deformation field information to enrich calibration data. The method is applied to a tensile test specimen and the material’s constitutive model, whose parameters are unknown a priori, is determined through an optimization process that compares these experimental measurements with iterative finite element simulations. The final parameters produce a simulation that tracks the local experimental displacement field to within a couple percent of error. Simultaneously, the percent error in the simulation for the load carried by the specimen throughout the test is less than one percent. The enriched calibration data is found to be sufficient to constrain model parameters describing anisotropy that could not be constrained by the global data alone.	en
dc.description.department	Aerospace Engineering	en
dc.format.mimetype	application/pdf	en
dc.identifier	doi:10.15781/T2N95Z	en
dc.identifier.uri	http://hdl.handle.net/2152/32930	en
dc.language.iso	en	en
dc.subject	Ductile failure	en
dc.subject	Plasticity	en
dc.subject	Inverse problems	en
dc.subject	Material characterization	en
dc.subject	FEM	en
dc.subject	In situ testing	en
dc.subject	Damage	en
dc.title	Towards the predictive modeling of ductile failure	en
dc.type	Thesis	en
thesis.degree.department	Aerospace Engineering	en
thesis.degree.discipline	Aerospace engineering	en
thesis.degree.grantor	The University of Texas at Austin	en
thesis.degree.level	Doctoral	en
thesis.degree.name	Doctor of Philosophy	en